1. Field of the Invention
The present invention relates generally to a method and apparatus for generating a template for use in assembling a structure such as a truss.
2. Related Art
Trusses and other large frame-like assemblies are normally assembled according to a template defined on a horizontal work surface. The usual method for fabricating a truss includes the steps of manufacturing the individual truss members required, positioning the truss members on a work surface where indicated by the template, and then joining the truss members together to form the truss. A key step in this process is the generation of a full-size template of the truss on the work surface according to which the individual truss members are positioned for assembly.
Known methods of generating a template include manually "drawing" the truss or portions thereof on the work surface. Alternatively, U.S. Pat. No. 4,514,899 discloses a method of assembling a wooden structure which includes forming an image of the structure on a transparency, superimposing an image of a rectilinear grid on the transparency over the image of the structure, and projecting the combined image of the structure and grid onto a movable assembly table, on which a reference grid is mapped. Alignment of the template on the work surface is achieved by alignment of the projected grid with the reference grid.
U.S. Pat. No. 4,739,487 discloses a method and apparatus for generating a template for use in the garment industry which includes storage of the coordinates of a plurality of patterns of garments or pieces thereof, displaying an image of a selected pattern onto a cutting table by means of a suitable video projection means, selecting the ideal position of the projected image on the cutting table, storing the optimal positioning data, and sending a command to cut the material from a sheet of material on the table.
There have also been attempts to improve methods of locating jigging hardware on a work surface. One such method used x-y data stored in a computer to repeatedly and sequentially direct a laser onto a series of single points on the work surface, at which points a worker marks the worksurface for later placement of jigging hardware. Also known are mechanical systems which moved and positioned locating pins around the worksurface.
Known methods of generating a full-size template for use in assembling relatively large structures such as a truss are problematic in that they require inordinate amounts of time and labor to produce. Moreover, known methods may require physical measurements over relatively large distances, which are difficult to perform with sufficient accuracy to achieve the design tolerances and strength of the structure. Methods known for generating smaller templates, optical projection methods for example, are not suitable for generating templates of larger structures due to the loss of resolution and distortion which result from the typically high enlargement ratio required to generate a full-size template.